#boot0cfg -t 55 -o noupdate ad0.-t 55 will give you an approximately 3 seconds delay, and noupdate will make the MBR read-only so that everytime it'll boot the current system so make sure you execute that command when logged in the system, not from a live cd or something.

#boot0cfg -t 55 -o noupdate ad0.-t 55 will give you an approximately 3 seconds delay, and noupdate will make the MBR read-only so that everytime it'll boot the current system so make sure you execute that command when logged in the system, not from a live cd or something.

Sorry i meant that currently without your suggestion it does not auto boot and requires manually intervention by pressing F1 to boot system

Reread my post. You must use the *device*, i.e. no slice number or partition. And remove the second -t 55 too.
But why don't you use fdisk? You only have one system, so you don't need any boot manager.